Reconfigurable optical add-drop multiplexers (ROADMs) have a multitude of uses and have shown great promise for use in optical systems. For example, one promising area of application for ROADMs is in the field of wavelength division multiplexed (WDM) light wave systems. ROADMs may be used for the selective broadcasting, dropping, and monitoring of discrete wavelengths.
In the field of optical systems, photonic integrated circuits (PICs) provide an integrated technology platform increasingly used to form complex optical systems. This technology allows multiple optical devices to be integrated on a single substrate. For example, PICs may comprise integrated amplifiers, receivers, waveguides, detectors, and other active and passive optical devices arranged in various configurations.
Asymmetric twin waveguide (ATG) technology has proven to be a promising method for optoelectronic integration and offers a relatively simple fabrication process for even the most complex PIC design. The ATG design significantly reduces modal interference by substantially confining different modes of light to propagation in different waveguides. Modal confinement is accomplished by designing waveguides such that the mode of light that propagates in a waveguide has a different effective index of refraction than the mode of light that propagates in the adjacent waveguide. This feature substantially isolates the light propagating in each waveguide, which lends itself to the specialization of functions performed by the waveguides. Transfer of light between the waveguides is facilitated by lithographically defined taper couplers. The minimal modal interference and efficient coupling result in high-performance lasers, p-i-n and avalanche photodiodes, SOAs, and integrated combinations of these fundamental photonic functionalities. U.S. Pat. Nos. 6,381,380, 6,330,387, 6,483,863, 6,795,622, and 6,819,814, the contents of which are hereby incorporated herein by reference in their entirety, provide a description of ATG and various embodiments of ATG.